How to work in exercise with an 8 month old

FTM here, 35, and out of shape. Our LO is teething majorly right now, needs lots of engagement, and I work FT, have two pets, and trying to balance all the adulting things alongside my SO.

I NEED to start exercising. I want to be healthy and energetic for my son, not to mention the up and down all day is killing my knees 😆

How do I even start?? All day I’m going from one thing to the next and the next and before I realize it, the day is over! I don’t even know what moves to work in. My core is so weak anymore. It’s hard to figure out where to begin. Who’s been there and overcome?? Who has learned a thing or two and wants to help a girl out. 🙏🏻